I am the lucky leader of a group that is only five years old, I have been there from day one! The most important thing that you need to do first is have a pow wow with your principal, set goals, talk about a mission. It is important that you both are on the same page from day one, you don't want to have your plan and then later find that your principal has something totally different!
From there set a meeting date, advertise,advertise, advertise that date! Dont get discourage from a low turnout. Make sure that meeting minutes get sent home, let everyone know what the goals are! Then send home a survey, get input on events, fundraising, ideas...yada yada.
Our group was ran by the principal the first four months then she asked me. When I became leader we started formalizing things, getting a tax id number, own checking account, things like that. We did not do bylaws, incorporate, become 501 until two years later. I look back and see that you need some time for it to grow before you jump into all of that paperwork, you want to concentrate on getting parents involved and then with all of that input you can move forward.
While you are starting make sure that you have a table at open house, K orientation (talk at that day) take pictures, do bulletin board, get that word out. If you have a warm body talk come talk about bringing one friend next time...you would be amazed at how that works.
My first meeting we had 5 people, I wanted nothing more than to be able to get 15 parents at a meeting by the last meeting of the month. I had four staff members come just to show that support, here it is five years later and we now average around 24-26 people! Our volunteer list ha sgrown to over 60 people...it takes time but you can make it happen. Step one;the PRINCIPAL !!!